Cohorts B and C will enroll patients with recurrent high grade gliomas or biopsy proven low grade glioma, respectively, who have residual measurable disease. Patients in cohorts B and C will be treated with crenolanib (CP-868,596) (300mg once daily on an empty stomach) continuously until they fulfill one of the criteria for study discontinuation. Magnetic resonance imaging (MRI) will be done to assess the tumor response as well as progression free survival (PFS). The primary endpoint for both cohorts B and C will be overall response rate according to the Response Evaluation Criteria In Solid Tumors (RECIST), as assessed by standard imaging modalities. In addition, 6-month Progression-free survival (cohort B) and 1-year PFS will also be assessed.